This morning, in a major setback to U.S. efforts in Afghanistan, almost 500 political prisoners--many of them Taliban fighters and commanders--escaped from the Sarposa prison in Kandahar through a tunnel in the second prison break orchestrated by the Taliban since 2008, when the group freed 1,200 prisoners in a suicide attack that killed 15 guards, according to The New York Times. An effort to recapture the escaped prisoners is underway. In the meantime, here's what we know about how the Taliban accomplished today's escape:

Prison guards discovered that prisoners in the institution's political wing were missing around 4 am, according to the Associated Press, but the Taliban claims the guards didn't discover the breach until closer to 7:30 am. In the photo above, an Afghan prison guard points to the hole that inmates used to escape through the tunnel.

The break came from without rather than within, according to the Taliban at least. Spokesman Zabiullah Mujahid explained in a statement that the Taliban worked for five months to dig a 320 meter-long tunnel into the prison that snaked below security checkpoints outside the facility and the Kabul-Kandahar highway (Afghan police, according to the Times, say the tunnel is more than 1,000 meters long). The militants launched the dig from a house "within shooting distance of the prison guard towers," the AP notes, but it's not clear whether they lived in the house as the dig continued. The head of Kandahar's prisons told The Guardian that constructing the tunnel must have been extremely labor-intensive given that the Taliban had to refrain from using heavy machinery that could attract attention to its efforts.

At 11 pm on Sunday night, per the Taliban's account, three Taliban prisoners who'd been informed of the plan ahead of time went from one cell to another, rousing several inmates at a time and escorting them to the tunnel. Mohammad Abdullah, who claimed he helped organize the escape from within the prison, told the AP that he and his associates got copies of cell keys from "friends"--suggesting that some prison guards may have acted as accomplices. The escape took place between 11 pm and 3:30 am, according to the Taliban, and one escapee told the BBC that it took him around 30 minutes to walk the full tunnel. When the prisoners emerged from the underground passageway, Taliban members greeted them and whisked them to waiting vehicles, which transported them to Taliban-controlled locations. As the prisoners boarded the vehicles, Taliban fighters and suicide bombers stood by in case security forces got wind of the scheme and tried to thwart the operation.

Update: The Daily Beast's Ron Moreau and Sami Yousafzai have a fascinating account of their interviews with two Taliban commanders who escaped today. One fighter explains how he feared the tunnel would collapse as he moved through it, while another notes that the prison break organizers confiscated the inmates' cell phones before they entered the tunnel to prevent them from informing people about their escape prematurely. The Daily Beast also learns that the Taliban dug their tunnel using pickups, tractor-pulled trailers, and donkey carts, and that the Taliban's original plan, aborted at the last minute, was for its suicide bombers to enter the jail after all prisoners had escaped and blow themselves up once prison security noticed the breach. "The escapees sounded more committed than ever to rejoin the fight," Moreau and Yousafzai observe.